1. Field of the Invention
The present invention pertains to techniques for selectively opening and closing flow passages. More particularly, the present invention is related to apparatus and methods for selectively closing flow passages along tubular members, and finds particular application in wells and the like wherein tubing strings, for example, must be selectively closed to permit various operations on the wells.
2. Description of Prior Art
A variety of operations necessary for proper completion and maintenance of a well is carried out using a tubing string lowered into the well, and which tubing string must at one time or another be closed at a location within the well. Such operations, for example, include washing the well perforations in the casing, formed at a formation from which production is anticipated, prior to gravel packing the well at that location, or at which fluid is to be injected as in the case of an acidizing operation, for example. In such instances, it has been the practice to utilize a ball catcher seat within the tubing string below the level of the wash tool or acidizing tool. Then, with the tool at the level of the formation of interest, a ball is circulated down the tubing string to establish sealing engagement with the catcher seat, whereupon fluid is pumped into the tubing string which is now closed by the ball and seat. Increased pressure within the tubing string may be utilized to operate the wash tool, for example, thus allowing the fluid pressure to emerge from the wash tool into the surrounding annular region within the casing of the well to carry out the desired operation. To reopen the tubing string, the ball must be reverse pumped out of the tubing string. Where the tubing string must simply be repositioned without reopening, a circulating valve may be included above the wash tool, for example.
A ball-and-seat arrangement to close the tubing string may be utilized with a variety of other tools to carry out hydraulic setting of such tools. For example, hydraulically set packers may be operated with such a ball-and-seat closing device, after PG,3 which, to reopen the tubing string, the ball must either be reverse pumped out of the well or otherwise disposed of.
In addition to the inconvenience of having to reverse pump a ball closure device from a well, such a device presents other problems. For example, where a wash tool is to be positioned within a well at the level of perforations in the casing, several attempts at locating the wash tool at the proper depth may be required. When such a tool is set, it sealingly engages the surrounding casing at locations above and below the wash outlets in the tool so that the washing, or acidizing, fluid may be confined longitudinally within the casing at the depth of interest. The operator at the surface can detect whether the tool is located at the perforations by observing the fluid pressure in the tubing string. If the fluid pumped into the tubing string is free to move through perforations in the casing into the surrounding formation, the fluid pressure may drop. If the tool is not properly placed and no perforations are available in the surrounding casing, the fluid pressure will not be permitted to drop by means of fluid communication into the surrounding formation. Then, the operator must release the fluid pressure and move the tubing string with wash tool attached. To so move the tubing string, if no flow valve is available, the operator must pump the ball out of the tubing string to allow fluid movement along the tubing string. This can be an expensive and time consuming operation. In any event, if the tubing string is to be reopened for fluid flow therethrough below the wash tool, the ball must be removed from the tubing string.
It is desirable and advantageous to provide a closure valve that is selectively operable for opening and closing passages along tubular members. In particular, such a closure valve would eliminate the need for a ball and catcher seat for use in tubing strings as described above, for example, and would permit the reopening of the flow passage along such a tubing string after operations requiring the closure of the flow passage are completed.